The present invention relates to a vacuum valve directly used for supplying working fluid such as source gas in physical and chemical machines and the like or used for reducing pressure in a vacuum chamber in which such source gas is used and more specifically relates to a vacuum valve having a heater and formed such that adhesion of a product from the working fluid to a valve member and the like is prevented by the heater.
In a manufacturing apparatus of a semiconductor, for example, high-temperature source gas is used for chemical treatment such as etching carried out in a vacuum chamber and a vacuum valve is used for supplying the source gas or for reducing pressure in the vacuum chamber. However, a product is likely to be precipitated out of the source gas when a temperature of the source gas becomes low and the product adheres to an inside of the vacuum valve, the valve member, and the like to reduce an opening/closing accuracy. Therefore, it is important that such a vacuum valve is formed to be able to prevent precipitation of the product out of the working fluid and adhesion of the product to the valve member and the like.
Therefore, conventionally, various vacuum valves with heaters in which a casing, a valve member, and the like are heated by a heater to prevent adhesion of a product are proposed. For example, there is one disclosed in Japanese Patent No. 3005449 in which a rod-shaped heater is mounted to a valve member for opening and closing a flow path and a lead wire of the heater is lead out of a casing through a hollow rod extending from the valve member is disclosed.
However, if the heater is mounted to the movable valve member and the lead wire of the heater is lead outside the casing as it is through the rod as described above, the lead wire is also displaced as the valve member operates and is drawn into or pushed out of the casing. Therefore, the lead wire is likely to be caught on or tangled with an end portion of a lead-through hole of the casing or other members, which tends to hinder opening and closing of the valve member. If the heater has a temperature sensor, a plurality of lead wires for the heater and the temperature sensor are provided and, as a result, the above-described problem is more likely to occur.
If a spiral portion for expansion and contraction is provided to the lead wire to absorb a displacement of the lead wire by expansion and contraction of the spiral portion, the above-described problem can be solved. However, if such a spiral portion is provided, the lead wire becomes long, weight of the lead wire increases, and the weight may adversely affect opening and closing operations of the valve member. If such a spiral portion is provided to a portion of the lead wire inserted through the rod, the spiral portion rubs against the rod every time the valve member opens and closes, the lead wire is likely to be damaged or worn out, and sliding resistance may adversely affect the opening and closing operations of the valve member.
It is a technical object of the present invention to prevent a lead wire extending from a heater from hindering opening and closing of a valve member in a vacuum valve in which the heater for preventing precipitation of a product out of working fluid is provided to the valve member for opening and closing a flow path.
To solve the above problem, there is provided a vacuum valve with a heater according to the invention, the vacuum valve comprising: a valve casing including a first main port, a second main port, a flow path connecting both the main ports, and an annular valve seat provided in the flow path; a cylinder connected to the valve casing; a poppet-type valve member provided in the valve casing to open and close the valve seat; a rod having a tip end portion connected to the valve member and a base end portion extending into the cylinder; a piston disposed for sliding in the cylinder and connected to the base end portion of the rod to be driven by an action of fluid pressure; one or more heaters and temperature sensors mounted to the valve member; a terminal block mounted to the piston to be displaced with the piston; a connector mounted to the cylinder; a heater primary conductor and a sensor primary conductor respectively extending from the heater and the temperature sensor, passing through the rod, and having tip ends connected to the terminal block; a heater secondary conductor and a sensor secondary conductor having one ends respectively connected to the heater primary conductor and the sensor primary conductor through the terminal block, having the other ends connected to the connector, and having a spiral portion for expansion and contraction at an intermediate portion.
According to the vacuum valve of the invention having the above structure, without directly drawing the heater primary conductor and the sensor primary conductor out of the cylinder, the primary conductors are drawn outside through the terminal block mounted to the piston, the connector mounted to the cylinder, and the secondary conductors connected between the terminal block and the connector. The spiral portion for expansion and contraction is provided to the secondary conductors and displacements of the primary conductors due to opening and closing of the valve member are absorbed by expansion and contraction of the spiral portion. As a result, the respective conductors are not drawn into or pushed out of the cylinder. Therefore, the respective conductors are not caught on or tangled with an end portion of a lead-through hole of the cylinder or other members and opening and closing operations of the valve member become stable. Because the spiral portion is provided to the secondary conductors which are not displaced with the valve member, weights of the secondary conductors do not adversely affect the opening and closing operations of the valve member. Moreover, because the spiral portion does not rub against the rod, the conductors are not damaged or worn out and sliding resistances of them do not adversely affect the opening and closing operations of the valve member at all.
According to a preferable structural form of the invention, the heater primary conductor and the sensor primary conductor are inserted into a common tube to form a cable-like primary conductor bunch which is inserted into the rod and the heater secondary conductor and the sensor secondary conductor are inserted into a common tube to form a cable-like secondary conductor bunch which is formed with the spiral portion.
According to this structure, a plurality of conductors are prevented from being locked on or tangled with each other and the opening and closing operations of the valve member are further stabilized.
According to a concrete structural form of the invention, the cylinder includes a driving-side pressure chamber communicating with an operating port on a front face side of the piston and a conductor housing chamber on a back face side of the piston, the terminal block is mounted to a back face of the piston in the conductor housing chamber, a lid body defining the conductor housing chamber is mounted to an end portion of the cylinder, the lid body is mounted with the connector and is provided with a hollow portion, and the spiral portion is housed in the hollow portion.
A coil-shaped return spring is provided between the lid body and the piston in the conductor housing chamber and is provided around a tube portion formed on the lid body to surround the hollow portion such that the return spring is isolated from the spiral portion by the tube portion.
With such a structure, it is possible to make effective use of the lid body to isolate the coil spring from the respective conductors and to reliably and efficiently prevent interference of them with each other.
In the invention, the valve casing further includes at least one of a second heating mechanism for heating an outer face of the valve casing and a third heating mechanism for coming in contact with the valve member in opening of the valve member to heat the valve member. The second heating mechanism includes a heat-transfer cover with which the outer face of the valve casing is covered, one or more second heaters mounted in the heat-transfer cover, and a heat insulating cover disposed around the heat-transfer cover while maintaining a gap therebetween, the third heating mechanism includes a heat-transfer body disposed in a fixed manner in such a position as to surround the rod in the casing, one or more third heaters mounted in the heat-transfer body, and a heat-transfer face formed at a tip end of the heat-transfer body, and the heat-transfer face is formed to come in contact with a heat receiving face of the valve member in opening of the valve member.